Two Buttes, CO., Mantle Evolution and Potassic Magmas

将通过研究科罗拉多州Two Buttes的钾质和镁铁质岩石来研究钾质火成岩的成因和次大陆地幔的演化。Two Buttes是美国西部最东端的新生代火成岩。这些岩石处于极端的地理位置，具有不寻常的成分，似乎位于一个厚厚的大陆根之上。将完成野外研究，确定年龄，并进行岩相学、电子探针、常量元素和微量元素以及同位素分析。主量元素和微量元素丰度以及Nd锶同位素丰度将与不同构造环境下的岩石进行对比，以检验岩浆成因理论、大陆岩石圈交代理论以及熔体生成与俯冲之间的关系。辉石结构类似于那些归因于岩浆混合的结构，同位素和化学研究将被用来调查这一过程在两个巴特岛和其他地方产生不同类型岩石的重要性。

The genesis of potassic igneous rocks and the evolution of the subcontinental mantle will be investigated by studying the potassic, mafic rocks at Two Buttes, Colorado, the easternmost Cenozoic igneous intrusives in the western U.S. These rocks are at an extreme geographic position, have unusual compositions, and appear to be above a thick continental root. Field studies will be completed, ages will be determined, and petrographic, electron probe, major and trace element, and isotopic analyses will be made. Major and trace element and Nd and Sr isotope abundances will be compared with those of rocks in contrasting tectonic settings to test theories for magma genesis, for metasomatism of continental lithosphere, and for relationships between melt generation and subduction. Pyroxene textures resemble those ascribed to magma mixing, and isotopic as well as chemical studies will be used to investigate the importance of the process in producing the diverse rock types at Two Buttes and elsewhere.